Phenolic compounds are useful for the synthesis of useful organic compounds such as couplers for colorant uses. Useful compounds include those having a substituted first amino group in the 2-position and a substituted second amino group in another position such as the 5-position of the phenol. One example of such useful compounds is a phenolic coupler useful as a cyan dye-forming coupler in a silver halide imaging process. Particularly useful phenolic compounds, which give the desired hue and absorption curve shape, are those containing the requisite two amino groups, including a ballast in one of the two groups, and a 6-chloro substituent. A ballast is a hydrophobic group having 8 or more aliphatic carbon atoms which serves to keep the coupler and resulting dye within the hydrophobic dispersion in which it is present so that it will not be washed out during the aqueous processes associated with development.
There have been available several processes for obtaining phenolic compounds bearing two amino substituents. In the first, a phenol is provided with an amine group in the 2-position and a nitro group in the other desired amino position. The 2-position is converted to the desired amino substituent using acid chloride. Then, the nitro group is reduced to amine and the second amine group is converted to the desired amino substituent using acid chloride. This method is limited in the order of introducing the amino substituents and methods for introducing the 6-chloro substituent. Further, it would be desirable to avoid the use of nitroaminophenol compounds for safety reasons since such materials present an explosion concern.
Another method is described in Begley, U.S. Pat. No. 6,201,125. The use of 2-alkyl-6-nitrobenzoxazoles is suggested to prepare 2,5-dicarbonamido phenols, but there is no indication of how to prepare the desired 6-chloro-2,5-dicarbonamido phenols.
In yet another method as described by Mitsunori Ono in “Heterocycles”, 27(4), 881, (1988). The use of 2-alkyl-6-nitrobenzoxazoles is suggested to prepare 2,5-dicarbonamido phenols but again there is no indication of how to prepare 6-chloro-2,5-dicarbonamido phenols. In addition, the examples employ a 2-t-butyl group, and it was found that an attempt to hydrolyze the oxazole ring in acid to unblock the 2-position was unsatisfactory and “all attempted usual acid cleavage . . . failed.” Ono is ultimately concerned with effecting a reaction at the 4-position of the phenol ring rather than effecting a conversion of the nitro group or introduction of a chloro group, so the use of alkaline KOH hydrolysis is of no concern. But if one does desire to convert the nitro group, as in the present case, there is a major concern, because the use of alkaline KOH unblocking will also initiate undesired side reactions at the converted nitro site.
It is desirable to develop a process that provides a simple and safe way to prepare 6-chloro-2,5-dicarbonamido phenol compounds in good yield.